Abundance and characteristics of microplastics in stormwater runoff from parking lots and roadways on a university campus

The release and profile of microplastics (MPs) in surface runoff from parking lots and roadways is poorly understood. Here, we quantified and characterized MPs in runoff samples ( n = 21) from the drainage outlets of two such areas at the University of Mississippi during two separate rain events. Samples were analyzed using a combination of optical microscopy and Fourier Transform Infrared micro-spectroscopy (µ-FTIR). MP concentrations (particles/L ± 1SE) at the onset of the storm event and after 30 minutes varied from 128 ± 114 to 8 ± 4 for the first event, and from 17.3 ± 3 to 6 ± 2.5 for the second event, respectively. Both rain events demonstrated the first flush phenomenon, where pollutants are readily washed from the surface in the early stages of runoff. Most of the particles (91%) ranged between 30-150 µm in size, with 30 µm being the lowest size measured. Irregular particles (fragments) were dominant (50%), followed by spherical particles (32%) and fibers (18%). The top abundant types of MPs detected were acrylonitrile butadiene styrene (12%), polycarbonate (12%), polyurethane (11%), polymethyl methacrylate (10%), polyethylene terephthalate (8%), polyvinyl chloride (7%), ethylene vinyl acetate (6%), ethylene propylene (6%), polyamide (5%) and polyacrylamide (4%). Sources of MPs include plastic litter that has fragmented and road wear particles that can include reflective coatings. Even with limited spatial and temporal sampling, these findings indicate that parking lots and roadways at the investigated sites serve as significant sources of MP pollution in stormwater runoff. Consequently, analogous sites merit examination to better characterize the scope and mechanisms of this environmental input.